Quite possibly the most annoying "Word" knows to the "English speaking nation." shortened, or "1137" way of saying "Not Much."
Its just that our time has gotten to lazy to type nothing much, which is stupid because if your not doing anything you should be able to type "Nothing much".

Quite Possibly the most useless internet/chat abbreviation known to man. 'nm' can be short for one of two things, 'Never mind' and 'Nothing much'.
Commonly misinterpreted by users, the abbreviation can be harmful, even fatal.

'Hey fag! You best not have spent all my money. What did you spend it on?'
'nm'
'Well I do fucking mind you worthless shit! It’s my bling! Ima come around and cut your balls off and put them in your mouth!'

The previous was a common occurrence where Person B merely stated that he had not wasted much Person A's money, however, he got dead because he used the vague term, 'nm'.

an annoying/lazy way of saying "Oh, I was just sitting here with my thumb up my ass, waiting for you to ask me what I was doing. In fact, let's just stand here and piss away 3 minutes of our lives talking in unclear ambiguous terms about how our day is, what we did five minutes ago, and what we plan on doing five minutes from now."

in the subject line of an e-mail, (nm) stands for no message. that is, the sender is so to the point that he needed only the subject line to express himself, so there's no need for the reader to open the (blank) message.